1. Field of the Invention
The invention relates to a motherboard and, more particularly, to a motherboard which can effectively utilize a memory module.
2. Description of the Related Art
A personal computer system is mainly composed of a motherboard, an interface card, and a peripheral device. The motherboard acts as a heart of the personal computer system. The motherboard not only has a central processing unit (CPU), a control chip set, and a slot where an interface card may be assembled, but also has some memory slots where memory modules may be assembled. One memory module is composed of several memory elements. The number of the memory modules assembled on the motherboard may be various according to a demand of a user.
FIG. 1 is a schematic diagram showing some elements of a conventional motherboard. A conventional motherboard 100 includes memory slots 111 to 116, an interface controller 120, and a system management bus 130. The memory slots 111 to 116 are used for allowing the memory modules (not shown) to be inserted in. Additionally, each of the memory slots 111 to 116 has three connection pins SA0 to SA2. Logic levels of the connection pins SA0 to SA2 correspond to access addresses of the system management bus 130 as shown in FIG. 2.
For example, when logic levels of the connection pins SA0 to SA2 is 000, the access address of the system management bus 130 is A0h. As a result, when the interface controller 120 wants to access the memory module inserted in the memory slot 111, the interface controller 120 reads corresponding data such as serial presence detect (SPD) data according to the access address A0h of the system management bus 130.
The access addresses of the system management bus 130 cannot be repeated. Consequently, the logic levels of the connection pins SA0 to SA2 of the memory slots 111 to 116 of the conventional motherboard 100 are different from each other. However, the SPD of some memory modules in the market only supports four addresses A0h, A2h, A4h, and A6h. That is, the connection pins SA2 of the memory slots 111 to 116 must be electrically connected with ground voltage to meet the four addresses A0h, A2h, A4h, and A6h supported by the memory module. As a result, when more than four memory modules are inserted in the memory slots 111 to 116 of the conventional motherboard 100, the access addresses of the system management bus 130 are repeated. Thus, the personal computer system cannot be booted normally.
Therefore, a warning light is utilized to timely remind the user that the number of this type of the memory modules inserted in the common motherboard cannot exceed four. However, in this mode, the number of this type of the memory modules inserted in the motherboard is at most four, and the memory slots of the common motherboard cannot be fully utilized. Another method is illustrated accompanying FIG. 3. A conventional motherboard 300 includes memory slots 211 to 216, an interface controller 220, a multiplexer 230, and system management buses 241 to 243.
As shown in FIG. 2 and FIG. 3, all connection pins SA20 to SA22 of the memory slots 211 to 216 of the conventional motherboard 300 are maintained at the logic levels corresponding to the access addresses A0h, A2h, A4h, and A6h. The logic levels of the connection pins SA20 to SA22 of the memory slots 211 and 212 are the same as those of the connection pins SA20 to SA22 of the memory slots 215 and 216, respectively.
To avoid that the access addresses of the system management bus 130 are repeated, the memory slots 211 to 214 are electrically connected with the system management bus 242, and the memory slots 215 and 216 are electrically connected with the system management bus 243. As a result, when the interface controller 220 accesses data from the memory slots 211 to 216 one by one via the system management bus 241, it transmits a control signal S31 to make the multiplexer 230 timely switch the system management bus 241 to the system management bus 242 or 243.
In other words, a multiplexer is additionally added to the conventional motherboard 300 to fully utilize the memory slots. At the time, the hardware cost of the conventional motherboard 300 is increased along with the addition of the multiplexer.